1. Field of the Invention
The present invention relates to a mobile Digital Video Broadcasting-Handheld (DVB-H) Convergence of Broadcasting and Mobile Service (CBMS) system, and more particularly to a method and an apparatus for providing handover-related information to a terminal trying to perform handover, by using Program Specific Information/Service Information (PSI/SI).
2. Description of the Related Art
The DVB-H CBMS is a service providing a more convenient function through combination of a mobile communication system and a digital TV broadcast service having an excellent mobile reception capability. As the digital televisions come into wide use in place of the analog televisions, viewers became capable of enjoying indoors a high quality screen of a High Definition Television (HDTV) class and high quality sound of a Compact Disc (CD) class. However, the variety of the modern society has changed the activity and life patterns of viewers and has generalized portable devices, such as mobile phones, Personal Digital Assistants (PDAs), notebook computers, etc. As a result, there has been rapid increase in demands for enjoyment of a television with a clear screen quality even while on the move. Further, there has been a trial to overcome the limitation of the broadcast networks having no uplink channel by connection to a mobile communication network. Such a trial has yielded the DVB-H CBMS.
The DVB-H CBMS system has been made for a reception terminal capable of using a mobile communication channel and includes the concept of handover supported by a cell-based wireless communication such as the conventional mobile communication system. However, the handover of the DVB-H CBMS is different from the handover of a mobile communication system. That is, in the handover of a mobile communication system, a network manages individual users and receives measurement reports for management of the network including the handover. However, in the case of a typical broadcast system, a broadcast provider provides services and content but does not manage all individual users. The information needed for the reception of the broadcasting is sent to all users through the broadcast network, and the broadcast system does not have a user management function. The handover of the broadcast network has a specific technological requirement, which differentiates it from the handover of the mobile communication system.
FIG. 1 is a block diagram illustrating a structure of a typical mobile digital video broadcast network system. The illustrated entities include logical entities that may be or may not be physically discriminated. These logical entities can be combined into one or more physical entities. Further, only the interfaces in relation to the core idea of the present invention are illustrated in FIG. 1.
The system illustrated in FIG. 1 is for the Digital Video Broadcasting-Convergence of Broadcasting and Mobile Service (DVB-CBMS), which is one standard for mobile broadcast terminals. Although the notification broadcasting structure of the DVB-CBMS is illustrated as an example in FIG. 1 for convenience of description, other mobile broadcast systems having a notification message function operate in similar ways.
Referring to FIG. 1, the Content Creation (CC) unit 110 is a provider of broadcast services, which include conventional voice/image broadcast services, file (music file or data file) download services, etc. When there is a problem or change in the supply of the broadcast services, the content creation unit 110 notifies a notification event creator within a broadcasting Service Application (SA) unit 120 of the change.
The service application unit 120 receives content data of the broadcast service from the content creation unit 110, generates broadcast service data by processing the content data into a type proper for the broadcast network (for example, streaming audio/video or movie download, etc.), generates standardized metadata necessary for Electronic Service Guide (ESG), and generates charge information according to users. Further, the service application unit 120 receives the notification of a change in the broadcast service from the content creation unit 110, transmits a notification event to the notification message creator disposed within a service management unit 115, and provides service guide property information used in generating the notification message to the notification message generator.
The service management unit 115 determines a schedule for transmission of the broadcast service supplied from the service application unit 120 and generates a service guide. The service management unit 115 is connected to a broadcast network 140 for providing the broadcast service and an interactive network 150 for supporting interactive communication.
The service management unit 115 manages service provision information (such as subscriber information for receiving the broadcast service and information about if a subscriber has purchased related contents) and device information about terminals receiving the broadcast service. Further, the service management unit 115 transmits user charge information to the service application unit 120 and provides the subscriber information, the service provision information, and device information to the broadcast network 140 and the interactive network 150.
The broadcast network 140 is a network for transmitting a broadcast service, as an example of which the DVB-H is described herein.
The interactive network 150 transmits a broadcast service on a one to one basis or interactively exchanges control information and additional information in relation to the reception of the broadcast service. For example, the interactive network 150 may be a conventional cellular network such as the 3GPP Wideband Code Division Multiple Access (WCDMA).
The terminal 160 can receive a broadcast service and may be connected with a cellular network according to its capability. As used herein, the present invention considers a terminal that can be connected with a cellular network.
The interfaces between blocks of the mobile broadcast system will now be described.
CBMS-x refers to an interface for transmission within a range of an IP datacast standard through the DVB-H, and X-x refers an interface for transmission out of the range of the IP datacast standard through the DVB-H. Specifically, CBMS-7 interface is an interface for transmission from the service application unit 120 to the service management unit 115, and CBMS-3 interface is an interface used when a message is transmitted from the service management unit 115 through the broadcast network 140 and a broadcasting channel to the terminal 160. CBMS-4 interface is an interface when the message transmitted from the service management unit 115 is provided to the terminal 160 through either a dedicated channel for the terminal 160 or a broadcasting channel provided by the interactive network 150. CBMS-6 interface is an interface between the service management unit 115 and the broadcast network 140, which is used in order to receive event information occurring in the broadcast network 140 or set a transmission path to be used in the broadcast network 140 by the service management unit 115. CBMS-1 interface is an interface for carrying a control signal of the broadcast network, which is transferred to the terminal. In the DVB-H, a control signal channel called Program Specific Information/Service Information (PSI/SI) corresponds to CBMS-1. The X-3 interface is an interface used for setting of a transmission channel between the service management unit 115 and the interactive network 150, the X-2 interface is an interface for setting of a transmission channel between the terminal 160 and the interactive network 150, and the X-1 interface is an interface for setting of a transmission channel between the content creation unit 110 and the service application unit 120.
When a user belonging to the DVB-H network has moved from the reference network to a neighbor network or to another IP platform, the new network or IP platform also must provide the service being viewed without interruption. The terminal must find the program, which the user was viewing before the handover, in the new network to which the terminal has moved, and must continue to receive the program. When the transport stream changes, the terminal must find out a transport stream providing the same service in the new network or IP platform to which the terminal has moved. When the transmission frequency changes, it is necessary to know frequency information of the neighbor network or IP platform. The information in order to perform the above process can be obtained from the PSI/SI provided by the DVB broadcast network. The handover process and method in this case will not be described in detail herein, and a detailed description thereof is found in “ETSI TR 101 211 Digital Video Broadcasting(DVB); Guidelines on implementation and usage of Service information (SI).”
FIGS. 2A and 2B are block diagrams illustrating a transmitter and a receiver for conventional mobile digital video broadcasting, respectively.
In the transmitter shown in FIG. 2A, a data IP stream 200 and an ESG IP stream 201, which are information to be transmitted, are input to a DVB IP encapsulator 212, and MPEG-related information 202 and service information 203 are input to a PSI/SI table generator 213. The DVB IP encapsulator 212 encapsulates the received data IP stream 200 and ESG IP stream 201 and then outputs the encapsulated data to a multiplexer 220. The PSI/SI table generator 213 generates a PSI/SI table based on the input MPEG-related information 202 and service information 203 and the information received from the DVB IP encapsulator 212 about whether the ESG has been updated, and then outputs the generated PSI/SI table to the multiplexer 220. The multiplexer 220 multiplexes the encapsulated IP stream input from the DVB IP encapsulator 212, the PSI/SI table input from the PSI/SI table generator 213, and the MPEG TV streams 210 and 211, and then outputs the multiplexed data to a DVB modulator 230. The DVB modulator 230 modulates the data from the multiplexer 220 and then transmits the modulated data through an antenna 240.
In the receiver shown in FIG. 2B, the signal received through an antenna 250 is demodulated by a DVB demodulator 251, and the demodulated signal is input to a demultiplexer 260. The demultiplexer 260 de-multiplexes the input signal and then outputs the de-multiplexed signals to a DVB IP decapsulator 270, an MPEG decoder 271, and a PSI/SI processor 272. The DVB IP decapsulator 270 restores the IP stream by de-capsulating the encapsulated IP data and then outputs the restored IP stream to an ESG processor 280 and a data processor 281. The ESG processor 280 and the data processor 281 output necessary information for the user to a user interface 290 by using the input IP stream. The MPEG TV streams 210 and 211 are decoded by the MPEG decoder 271 and are then output to the user interface 290. Finally, from among the PSI/SI information input to the PSI/SI processor 272, the information necessary for the MPEG decoding is provided to the MPEG decoder 271 while other information is output to an adjustment unit 282. The adjustment unit 282 determines if handover is necessary, by referring to the PSI/SI information and by collecting the handover-related information distributed in each table. If handover is necessary, the adjustment unit 282 informs a broadcast reception controller 252 of the handover-related information. The broadcast reception controller 252 controls the DVB demodulator 251 in order to receive the broadcasting signal. That is, when the handover is performed, the broadcast reception controller 252 performs operations for controlling the DVB demodulator 251. For example, the broadcast reception controller 252 measures the reception intensity of a received broadcasting signal from a neighbor cell and may change the reception frequency of the receiver according to the changed frequency. Further, the broadcast reception controller 252 outputs necessary information to the user interface 290 by using the received service information.
FIG. 3 is a flow diagram illustrating a conventional handover process of a receiver.
Referring to FIG. 3, when the terminal has started to operate in step 300, the terminal receives a broadcasting signal in step 310. Then, in step 320, the terminal displays a service selected by a user on a screen after restoring a signal of the service through demodulation and decoding of the signal. After completing step 320, the terminal performs steps 330 and 340. Although steps 330 and 340 are sequentially presented in the specification and the drawing for convenience of description, it goes without saying that they can be simultaneously performed with step 320 in which the service is restored.
Steps 330 and 340 correspond to steps in which the adjustment unit 282 of FIG. 2B collects information necessary for the handover from among the information received from the PSI/SI processor 272. From among the information included in the PSI/SI, the handover-related information is mainly distributed in the Network Information Table (NIT) and the Service Description Table (SDT). Therefore, the receiver can collect the handover-related information in steps 330 and 340.
Thereafter, the receiver performs step 350 in order to determine if it is necessary to perform the handover. If it is determined in step 350 that the handover is unnecessary, the receiver returns to step 310 in which the receiver receives a broadcasting signal. If it is determined in step 350 that the handover is necessary, the receiver measures the reception intensity of neighbor cells and selects an optimum signal in step 360. Then, in step 370,-the receiver adjusts the frequency. Step 370 corresponds to a step for adjustment including the frequency adjustment, in order to receive a broadcasting signal from a new cell. Thereafter, in step 380, the receiver determines if reception of the new broadcasting signal is a success. When the reception of the new broadcasting signal is a success, the receiver returns to step 310 and performs the process again from step 310. When the reception of the new broadcasting signal is a failure, the receiver proceeds to step 390 in which the receiver terminates the process.
According to the conventional handover process as described above, even when a mobile digital video broadcasting receiver changes its position, a user of the mobile digital video broadcasting receiver can use a service selected by the user without interruption by handover. However, in the case of the conventional handover process, because the information for the handover is distributed in each table of the PSI/SI, the receiver must collect the information for the handover by referring to each table. Moreover, the conventional handover uses service IDs in order to identify the selected services during the handover. Generally, different networks allocate different service IDs to the same service.